probably dns/sni logs? with most sites using https that's all they're really going to get.
What about android?
probably doesn't matter because regular dns is performed in the clear. There's nothing preventing them from logging/intercepting your requests even if you changed them.
>Odd that iPhones let you change it for wifi, but not cellular.
>What about android?
AFAIK on both changing DNS can be done by using an app that acts like a VPN, and intercepts the DNS requests.
The latter could be construed as necessary logging while the former is spying for the sake of spying.
Network Settings -> Advanced -> Private DNS
Enter one.one.one.one (or substitute your favorite DoH-supporting resolver)